What Is Multiple Sclerosis?

Multiple sclerosis, or MS, is a disease of the central nervous system (CNS), the main network of nerves that carry electrical impulses throughout the body.

The CNS is made up of the brain and spinal cord. Both have nerve fibers that transport electrical messages from the brain to the rest of the body.

The nerve fibers are wrapped in a fatty tissue called myelin, which helps transmit the messages.

In multiple sclerosis, the myelin sheath which covers nerve fibers becomes inflamed and gradually is destroyed, leaving areas of patchy scar tissue (sclerosis) that disrupts communication between the brain and other parts of the body.

In addition, the underlying nerve fibers can also be damaged or destroyed.

This destruction of the myelin sheath and the damage to the underlying nerves can lead to a wide variety of symptoms that include numbness or tingling, balance problems, weakness, muscle spasms and blurred vision.

MS is a complex, unpredictable, and progressive disease. In some people, it can cause relatively few symptoms.

Others experience intermittent attacks. In the worst cases, people who have multiple sclerosis can lose the ability to speak, walk or write.

However, the disease does not seem to significantly shorten a person's life, and many people with multiple sclerosis are able to remain active.

But there is increasing evidence that the body's immune system plays a prominent role in its development, and some scientists think MS is an autoimmune disease.

The immune system, which usually protects the body by fighting germs and foreign bodies, may attack the myelin in the central nervous system.

Some researchers suspect that these attacks may be triggered by certain kinds of viral infections.

Researchers have also observed that some groups of people are much more susceptible to MS than others.

This suggests that there may be a genetic component to the disease.

Different Types of Multiple Sclerosis

The exact course of the disease in individual patients is unclear, too. MS affects people in a variety of ways.

In general, though, the disease follows several known patterns. Doctors group four of the patterns together under the heading "chronic progressive MS":

Relapsing-remitting MS (RRMS): In this pattern, the patient experiences MS as a series of actively symptomatic periods, called attacks, exacerbations, or relapses. These attacks are followed by quiet periods called remissions during which symptoms become much less severe and no obvious progression of the disease is observed. People may have a period of stability that lasts months or years before the pattern of relapses and remissions returns. According to the National MS Society, about 85 percent of people with MS are diagnosed with a relapsing-remitting course of the disease.

Primary-progressive MS (PPMS): This pattern is marked by a gradual worsening of symptoms. Patients generally do not experience acute exacerbations. While there are no distinct remissions, patients with PPMS may have temporary plateaus during which symptoms lessen somewhat. About 10 to 15 percent of people with MS are diagnosed with PPMS.

Progressive-relapsing MS (PRMS): In this pattern, patients experience gradual progression of disease that is accompanied by acute exacerbations as well. About 5 percent of people with MS have PRMS.

In addition, the National Institute of Neurological Disorders and Stroke estimates that up to 20 percent of people with MS have a benign form of the disease.

After the initial attacks, symptoms progress very little over the course of a person's lifetime.

A small number of patients have malignant MS, which is marked by a rapid decline that leads to disability and possibly death.

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